This invention relates to an electrolytic process for producing tetraalkyl 1,1,2,2-ethenetetracarboxylates. Such carboxylates can be used as coating for polycarbonates which enhances their clarity and hardness.
It has been disclosed by G. I. Nikishin et al in Izo. Ahad. Nank. SSSR, Ser. Khim. 9, 2154 (1984) that tetramethyl 1,1,2,2-ethenetetracarboxylate can be produced electrolytically in an electrolysis medium containing dimethyl malonate, methanol and a sodium iodide electrolyte. The anode and cathode used were, respectively, platinum and iron. A current density of about 220 mA/cm.sup.2 was applied through the electrolysis medium and a current efficiency of 60% was reported. However, an attempt by Applicant to duplicate this work produced extensive amounts of degradation products and only a current efficiency of about 10% for tetramethyl 1,1,2,2-ethenetetracarboxylate. The extensive production of the degradation products was believed to be the result of the extremely high current density called for by G. I. Nikishin et al.
The use of lower current densities and a resultant lowering of the production of degradation products is shown in U.S. Pat. No. 4,076,601 wherein it is taught that tetramethyl 1,1,2,2-ethanetetracarboxylate is produced in an electrolysis medium of dimethyl malonate, methanol and an iodide electrolyte. The electrolysis is conducted at a temperature of 50.degree. C. or above. Current efficiencies above 65% for the saturated carboxylate product are reported. However, the current efficiency for tetramethyl 1,1,2,2-ethenetetracarboxylate is shown to be in the range of about 3-5%.
It is therefore an object of this invention to provide an electrolytic process for the production of tetraalkyl 1,1,2,2-ethenecarboxylate with low concomitant production of degradation products and with high current efficiencies for such unsaturated carboxylates.